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Cnidarians/Transcript
Transcript Text reads: The Mysteries of Life with Tim and Moby. A man, Tim, is shown wearing a diving helmet. He is exploring underwater. MOBY: Beep. TIM: Aaah! A robot, Moby, pops up from behind a large rock structure to scare Tim. Moby hands Tim a letter. Tim is heard reading from a typed letter. TIM: Dear Tim & Moby, I think jellyfish are cool! What can you teach me about them? From Newt. TIM: Jellyfish belong to a phylum of invertebrate aquatic animals called cnidarians. An image shows a group of five cnidarians. One resembles a small tree. Another is an irregular sphere with small spikes. Another is saucer shaped with tentacles. Another has a columnar body with tentacles coming out of its top. Another has a tubular shaped body. A circular opening is at its top. This opening is surrounded by tentacles. MOBY: Beep. TIM: Oh, an invertebrate is an animal with no backbone or spinal column. The screen is divided into two equal sections. In one section, an image shows an animated X-ray of a person showing only the spinal column. This section is labeled “vertebrates.” In the other section, an image shows the X-ray of a cnidarian with a tubular shaped body. There is no spinal column. This section is labeled “invertebrates.” TIM: Cnidarians are very simple creatures—they typically have only two cell layers. An animation shows a cnidarian with a tubular shaped body cut in half. The center of this tubular body is hollow. TIM: Cnidarians come in two basic shapes: medusa and polyp. TIM: But they both have radial symmetry, meaning that if you sliced one down the middle at any point in its body, both sides would be the same. The screen is divided into two equal sections. In one section, an image shows a circular shape. Inside, there are four oval shapes. Three dotted lines are dividing the shape into six equal sections. Each line travels through its center. Text reads: medusa. In the other section, an image shows a figure that resembles the sun. Three dotted lines are dividing the shape into six equal sections. Each line travels through its center. Text reads: polyp. TIM: All cnidarians have tentacles radiating out from a central mouth. Medusas are weak swimmers, relying mainly on water currents to move them along. An animation shows a cnidarian that is saucer shaped with tentacles swimming through the water. TIM: And polyps don’t move at all–they’re sessile. That means they attach themselves to something else, like a rock or the ocean floor. An animation shows a cnidarian that has a tubular body swaying in the current. MOBY: Beep. TIM: Well, there are lots of different kinds of cnidarians! They include jellyfish, anemones, coral, hydras, and my personal favorite, the Portuguese man-of-war. An image shows the darkened shapes of five cnidarians. Each shape is illuminated as its name is said. One resembles a small tree. It is labeled “coral.” Another is saucer shaped with tentacles. It is labeled “jellyfish.” Another has a columnar body with tentacles coming out of its top. This is labeled “anemones.” Another has a tubular shaped body. A circular opening is at its top. This opening is surrounded by tentacles. It is labeled “hydras.” Another resembles a helmet with a short fin running down the center. At one end, there is a group of tentacles. This is labeled “Portuguese man-of-war.” MOBY: Beep. TIM: Yeah, you don’t want to get too close to these animals. Cnidaria is Latin for “stinging cells,” and there’s a good reason for the name. An animation shows a swimming jellyfish. TIM: A cnidarian’s tentacles are lined with microscopic stinging structures called nematocysts. Each nematocyst contains a coiled up tube that can shoot out like a harpoon. The screen zooms into one of the jellyfish tentacles. An oval shape is shown. Inside the oval, a wrapped up narrow tube is attached to a two-pronged spike. TIM: When a passing animal touches a cnidarian’s tentacles, the nematocysts shoot out and attach to the animal. An animation shows a fish rub against a jellyfish tentacle. The two-pronged spike shoots out and attaches to the fish. TIM: The tentacles draw the prey into the cnidarian’s mouth. The fish is slowly pulled up the jellyfish tentacles toward the center of its body. TIM: Some nematocysts contain poison that stun prey. This is the same stuff that causes us to be stung by jellyfish. Anyway, food is broken down inside the cnidarian’s body cavity. And since they have only one opening, cnidarians also expel waste from their mouths. An animation shows the skeleton of the fish inside the body of the jellyfish. The skeleton is shown falling from the center of the jellyfish’s body. MOBY: Beep? TIM: Yeah, I don’t know if that gives them bad breath. Polyps and medusas also have different ways of reproducing. Medusas reproduce sexually: females release eggs into the water, and males fertilize the floating eggs. An animation shows a jellyfish swimming. The jellyfish releases a transparent blob into the water. Another jellyfish hovers over the blob. TIM: But polyps reproduce asexually in a process called budding. In budding, a polyp will grow a small new outgrowth, or bud, that eventually falls off and becomes a separate organism with the same genetic material as the original. An animation shows a hydra. A smaller, identical hydra grows out of its side and falls off, floats away, and attaches to the ocean floor. TIM: Some cnidarians go through both polyp and medusa stages in their life cycles. So they reproduce sexually in the medusa stage, and asexually in the polyp stage! An image shows a circular flow chart. An arrow is pointing from a jellyfish that is labeled “medusa,” to a circle labeled “egg.” An arrow is pointing from the egg to an irregular oval shape labeled “planula.” An arrow is pointing from the planula to a tube labeled “polyp.” An arrow is pointing from the polyp to a hydra. A final arrow completes the circle and points from the hydra to the jellyfish. An animation shows both Tim and Moby surface. MOBY: Beep! TIM: Yeah, it’s pretty cool. By the way, if you see a jellyfish while you’re swimming, stay away from it! An animation shows a figure that resembles a jellyfish floating toward Moby. MOBY: Beep. TIM: Uh, okay, stay calm … Um, I think we’re safe from this one. Tim grabs the figure to reveal that it is a plastic sandwich bag. Category:BrainPOP Transcripts Category:BrainPOP Science Transcripts